1. Field of the Invention
The present invention relates to: a surface inspection apparatus that detects the intensity of reflected light of inspection light irradiated on a surface of an inspection object and, based on the detected intensity of the reflected light, inspects the surface of the inspection object; a surface inspection apparatus that inspects for defects, such as foreign matter and scratches, that are present on the inner circumferential surface of a cylindrical body, which is the inspection object; or a surface inspection head apparatus that inspects the surface of the inspection object.
2. Related Art
A known example of an apparatus that inspects the inner circumferential surface of a cylindrical inspection object is a surface inspection apparatus (e.g., refer to JPA H11-281582) that feeds a shaft shaped inspection head in an axial direction while rotating it therearound in order to insert it inside of the inspection object, irradiates the inspection object with inspection light from the outer circumference of that inspection head, successively scans the inner circumferential surface of the inspection object from one end to the other in its axial directions, receives light reflected by the inspection object through the inspection head in accordance with that scan, and, based on the intensity of that received reflected light, determines the state of the inspection object, e.g., whether any defects and the like are present. In addition, among surface inspection apparatuses of the type discussed above, there is one that can inspect the inner circumferential surface of a cylindrical body, such as a cylinder liner or a cylinder bore of an internal combustion engine, by projecting inspection light thereto, inserting a rod shaped inspection head, which is configured so that it receives light reflected by the inner circumferential surface, inside the cylindrical body, and then advancing and retracting the inspection head, relative to the cylindrical body, in its axial directions while rotating it around its axis, which extends in the longitudinal direction. Such an inspection apparatus generates a two dimensional image, based on the intensity of the reflected light, that corresponds to the inner circumferential surface, and then determines whether there are any defects on the inner circumferential surface based on the presence of dark areas in that two dimensional image.
In addition, with the surface inspection apparatus discussed above, a head apparatus, which is provided with optical path modifying members such as a mirror and a prism, is built into the interior of a head tube, wherein an opening is formed so that inspection light can pass therethrough to the outer circumference. With this head apparatus, the optical path of the inspection light is changed by the optical path modifying member so that it leads to the opening of the head tube, the reflected light of the light that emerges from that opening and impinges the surface of the inspection object enters the head tube from the opening, and the reflected light optical path is modified by the optical path modifying members so that it goes in the reverse direction of the inspection light, and thereby the light needed to inspect the surface of the inspection object for scratches, foreign matter, and the like is guided from the head tube to a light receiving part of the surface inspection apparatus. Rotating the head tube makes it possible to scan the inspection light over the entire circumference of the inner circumferential surface of a cylindrical inspection object in the circumferential direction. To protect the interior of the head tube from contamination, a protective window member is provided to the opening of the head tube so that the front surface and the rear surface of the protective window member are orthogonal to the optical path of the inspection light.
The surface inspection apparatus discussed above comprises a detecting means that is configured so that a plurality of light receiving fibers, which receive reflected light, are adjoined around a light projecting fiber, which projects inspection light, and so that these optical fibers are held by a fiber holding tube. With this detecting means, the positional relationship between the light projecting fiber and the light receiving fibers, e.g., the distance therebetween, is fixed, and therefore the sensitivity characteristic of the detecting means with respect to changes in the properties of the reflected light, such as its direction or intensity, is also fixed. Because the type of defect present in the inspection object characterizes the property of the reflected light, the position and the like of the light receiving fibers in a conventional surface inspection apparatus are set so that the detecting means is provided with a sensitivity characteristic that can sense the defects for which the inspection object is to be inspected.
Thus, with a conventional surface inspection apparatus, the sensitivity characteristic of the detecting means is fixed so that it is possible to sense the defect to be detected, which is a problem because if, for example, there is a change in the type of defect to be detected, then that defect cannot be adequately sensed; in addition, if locations that are to be distinguished from defects are newly set, then those locations will be mistakenly detected as defects.
In addition, if the surface inspection apparatus discussed above is used to inspect the inner circumferential surface of a cylindrical body, then the rotational axis of the inspection head and the center line of the cylindrical body must be made to coincide. As long as they coincide, the inspection head and the inner circumferential surface of the cylindrical body will always oppose one another, regardless of the rotational position of the inspection head, which makes it possible to receive reflected light of the same intensity provided that the intensity of the inspection light is constant and the properties of the inner circumferential surface are uniform. However, if the rotational axis of the inspection head and the center line of the cylindrical body do not coincide, then the angle of incidence of the inspection light will vary with the rotational position of the inspection head, which will change the intensity of the reflected light even if the properties of the inner circumferential surface are uniform.
In that case, with every rotation of the inspection head, there are two occasions when the inspection head and the inner circumferential surface oppose one another, and the angle of incidence varies gradually at times when they are not opposed, and therefore the intensity of the reflected light fluctuates. Consequently, when a two dimensional image is generated that has a density that is in accordance with the intensity of the reflected light, that two dimensional image is brightest at the position where the inspection head and the inner circumferential surface oppose one another, and is relatively darker elsewhere with a density (brightness and darkness) that varies periodically. If by chance there is a dark area, which corresponds to a defect, present in the relatively bright portion of the two dimensional image, then there will be no error in determining that it is a defect; however, if that dark area is present in a relatively dark portion, then the contrast around the dark part will be low, which increases the possibility of an error in determining that it is a defect.
In addition, if the protective window member is provided to the opening in the head apparatus discussed above, then, when the inspection light passes through the protective window member and emerges on the outer side of the head tube, the inspection light will be reflected by the front surface and the rear surface of the protective window member. This reflected light will return in a direction that is the reverse of that of the inspection light because of the optical path modifying members, and consequently the light reflected by the inspection object and the light reflected by the protective window member will be superimposed with the light detected by the surface inspection apparatus, which hinders the improvement of sensitivity.